John Gill Commentary 1 Kings 20:41

"And he hasted, and took the headband away from his eyes; and the king of israel discerned him that he was of the prophets." — 1 Kings 20:41 (ASV)

And he hasted, and took away the ashes from his face
Took off the linen cloth from his eyes, unveiled or unmasked himself:

and the king of Israel discerned him, that he was of the prophets ;
he knew him again, having seen him once or twice before; otherwise there could be nothing in his face that could discover him to be a prophet, rather he was to be known by his habit.